Motor control device, motor control method, motor module, and electric power steering device

ABSTRACT

A motor control device includes a torque controller to operate based on a steering torque and to give an input to a control target that is a motor, and a model following controller to generate a first correction torque based on an output from the control target. A model following controller includes a high-pass filter to remove a low frequency component from a first correction torque, a friction compensation calculator that is coupled in parallel to the high-pass filter to apply friction compensation to the first correction torque to calculate an estimated value of a mechanical friction torque, and an adder to add the estimated value of the friction torque to the first correction torque from which the low frequency component is removed by the high-pass filter to generate a second correction torque and feed back the second correction torque to an input to the control target.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Applications No. 2021-160026 and 2021-160027, filed onSep. 29, 2021, and Japanese Patent Application No. 2021-214761, filed onDec. 28, 2021, the entire contents of which are hereby incorporatedherein by reference.

1. FIELD OF THE INVENTION

The present disclosure relates to a motor control device, a motorcontrol method, a motor module, and an electric power steering device.

2. BACKGROUND

A general automobile has an electric power steering device (EPS)including an electric motor (hereinafter, referred to simply as a“motor”) and a motor control device. The electric power steering deviceis a device that assists a driver's steering wheel operation by drivingthe motor. In the related art, the motor output according to a steeringtorque is realized by torque control, thereby assisting a steering wheeloperation.

Conventionally, a technique related to disturbance observer control isknown. A robust controller for reducing the influence of a disturbanceor a parameter variation of a control target on steering control isconventionally used. A conventional resonance point disturbancecontroller including a disturbance observer is used to suppress aresonance point disturbance excited at a resonance point of a suspensionin a front-rear direction. There is also known a technique forgenerating an appropriate steering reaction force without discomfortaccording to a road surface reaction force by eliminating a frictiontorque generated by internal friction of a steering mechanism.

It is desirable to improve the steering feeling that the driver can feelwhen assisting the steering wheel operation of the driver.

In recent years, market demands for noise, vibration, and harshness(NVH), for which there is one standard used for evaluation of comfort ofautomobiles, have become increasingly strict. However, the conventionaltorque control is particularly susceptible to a high frequencydisturbance and cannot suppress high frequency torque fluctuations, andthus it is difficult to meet market demands.

In the related art, a friction model as a function of an angularvelocity co of a motor is constructed, and friction compensation controlis performed using the constructed model. However, in general frictioncharacteristics, there is a problem that chattering is likely to occurbecause the sign of the friction torque is rapidly inverted around thetime when the angular velocity ω of the motor is zero.

SUMMARY

A non-limiting example embodiment of the present disclosure provides acontrol device usable in an electric power steering device including amotor to control the motor and includes a torque controller to operatebased on steering torque and to provide an input to a control targetthat is the motor, and a model following controller to generate a firstcorrection torque based on an output from the control target. The modelfollowing controller includes a high-pass filter to remove a lowfrequency component from the first correction torque, a frictioncompensation calculator coupled in parallel to the high-pass filter toapply friction compensation to the first correction torque to calculatean estimated value of a mechanical friction torque, and an adder to addthe estimated value of the friction torque to the first correctiontorque from which the low frequency component is removed by thehigh-pass filter to generate a second correction torque and feed backthe second correction torque to an input to the control target.

In a non-limiting example embodiment of the present disclosure, a motormodule includes a motor and the control device described above.

In a non-limiting example embodiment of the present disclosure, anelectric power steering device includes the motor module describedabove.

In a non-limiting example embodiment of the present disclosure, acontrol method of the present disclosure is a computer-implementedmethod for an electric power steering device including a motorcontrolling the motor. The method includes acquiring a steering torque,determining an operation amount based on the steering torque andinputting the operation amount to a control target that is the motor,generating a first correction torque based on an output from the controltarget, removing a low frequency component from the first correctiontorque, applying friction compensation to the first correction torque tocalculate an estimated value of a mechanical friction torque, adding theestimated value of the friction torque to the first correction torquefrom which the low frequency component is removed to generate a secondcorrection torque, and feeding back the second correction torque to aninput to the control target.

The above and other elements, features, steps, characteristics andadvantages of the present disclosure will become more apparent from thefollowing detailed description of the example embodiments with referenceto the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a configuration exampleof an electric power steering device according to an example embodimentof the present disclosure.

FIG. 2 is a block diagram illustrating a typical example of aconfiguration of a control device according to an example embodiment ofthe present disclosure.

FIG. 3 is a functional block diagram illustrating a function of aprocessor to control a motor according to an example embodiment of thepresent disclosure.

FIG. 4 is a functional block diagram illustrating a configurationexample of a model following controller in the first implementationexample.

FIG. 5 is a graph illustrating a gain characteristic T(s) of Q(s)·HPF(s)and a gain characteristic of a reciprocal of a modeling error Δ(s)between a plant and a nominal model P_(n)(s).

FIG. 6 is a graph illustrating a gain diagram of a transfer functionC(s) of a phase compensator in a torque controller.

FIG. 7 is a graph illustrating a gain diagram of a transfer functionHPF(s) of a high-pass filter.

FIG. 8 is a graph illustrating a gain diagram of a nominal modelP_(n)(s).

FIG. 9 is a graph illustrating measurement results of a steering angleand a torsion torque in a case where model following control is notapplied.

FIG. 10 is a graph illustrating measurement results of a steering angleand a torsion torque in a case where model following control is applied.

FIG. 11 is a graph illustrating a measurement result of a temporalchange of a steering angle in each of a case where the model followingcontrol is not applied and a case where the model following control isapplied.

FIG. 12 is a functional block diagram illustrating a configurationexample of a model following controller in the second implementationexample.

FIG. 13 is a graph illustrating simulation results of a steering angleand a steering torque in each of a case where friction compensationcontrol is not applied and a case where friction compensation control isapplied.

FIG. 14 is a graph illustrating simulation results of a steering angleand a steering torque in each of a case where the conventional frictioncompensation control is applied and a case where the frictioncompensation control according to the second implementation example isapplied.

DETAILED DESCRIPTION

With reference now to the accompanying drawings, example embodiments ofmotor control devices mounted on electric power steering devices of thepresent disclosure, motor control methods, motor modules including thecontrol devices, and electric power steering devices including the motormodules will be described in detail. However, needlessly detaileddescriptions may be omitted. For example, detailed descriptions ofwell-known matters and duplicate description of substantially the sameconfiguration may be omitted. This is because of avoiding the followingdescription redundant more than necessary and facilitating theunderstanding of a person skilled in the art.

The following example embodiments are merely examples, and a motorcontrol device mounted on the electric power steering device accordingto the present disclosure and a motor control method are not limited tothe following example embodiments. For example, the numerical values,the steps, the order of the steps, and the like illustrated in thefollowing example embodiments are only illustrative, and variousmodifications can be made unless any technical inconsistency occurs. Theexample embodiments or examples described below are merely examples, andvarious combinations are possible as long as no technical contradictionoccurs.

FIG. 1 schematically illustrates a configuration example of an electricpower steering device 1000 according to the example embodiment of thepresent disclosure.

The electric power steering device 1000 (hereinafter, referred to as an“EPS”) includes a steering system 520 and an assist torque mechanism 540which generates an assist torque. The EPS 1000 generates the assisttorque for assisting the steering torque of the steering systemgenerated when a driver operates a steering wheel. The assist torquereduces an operation load on the driver.

The steering system 520 includes, for example, a steering wheel 521, asteering shaft 522, universal joints 523A and 523B, a rotation shaft524, a rack-and-pinion mechanism 525, a rack shaft 526, left and rightball joints 552A and 552B, tie rods 527A and 527B, knuckles 528A and528B, and left and right steered wheels 529A and 529B.

The assist torque mechanism 540 includes a steering torque sensor 541, asteering angle sensor 542, an automobile electronic control unit (ECU)100, a motor 543, a deceleration gear 544, an inverter 545, and atorsion bar 546, for example. The steering torque sensor 541 detects asteering torque in the steering system 520 by detecting the amount oftorsion of the torsion bar 546. The steering angle sensor 542 detects asteering angle of the steering wheel. Incidentally, the steering torquemay be an estimated value derived from calculation, not a value of thesteering torque sensor. The steering angle can also be calculated basedon the output value of the angle sensor.

The ECU 100 generates a motor driving signal based on the detectionsignals detected by the steering torque sensor 541, the steering anglesensor 542, a vehicle speed sensor (not illustrated) mounted on avehicle, and the like to output the motor driving signal to the inverter545. For example, the inverter 545 converts direct-current power intothree-phase alternating-current power having U-phase, V-phase, andW-phase pseudo sine waves in accordance with the motor driving signaland supplies the power to the motor 543. The motor 543 is, for example,a surface permanent-magnet synchronous motor (SPMSM) or a switchedreluctance motor (SRM), and is supplied with the three-phasealternating-current power to generate assist torque according to thesteering torque. The motor 543 transmits the generated assist torque tothe steering system 520 via the deceleration gear 544. Hereinafter, theECU 100 will be referred to as a control device 100 for the EPS.

The control device 100 and the motor are modularized and manufacturedand sold as a motor module. The motor module includes the motor and thecontrol device 100 and is suitably used for the EPS. Alternatively, thecontrol device 100 may be manufactured and sold as a control device forcontrolling the EPS independently of the motor.

FIG. 2 illustrates a typical example of the configuration of the controldevice 100 according to the example embodiment of the presentdisclosure. The control device 100 includes a power supply circuit 111,an angle sensor 112, an input circuit 113, a communication I/F 114, adriving circuit 115, a ROM 116, and a processor 200, for example. Thecontrol device 100 can be realized as a printed circuit board (PCB) onwhich these electronic components are implemented. The control device100 is used to control a motor of an electric power steering deviceincluding the motor.

A vehicle speed sensor 300, the steering torque sensor 541, and thesteering angle sensor 542 mounted on the vehicle are communicablyconnected to the processor 200, and the vehicle speed, the steeringtorque, and the steering angle are transmitted from the vehicle speedsensor 300, the steering torque sensor 541, and the steering anglesensor 542 to the processor 200, respectively.

The control device 100 is electrically connected to the inverter 545(see FIG. 1 ). The control device 100 controls switching operations of aplurality of switching elements (for example, MOSFETs) included in theinverter 545. Specifically, the control device 100 generates a controlsignal (hereinafter referred to as a “gate control signal”) forcontrolling the switching operations of the respective switchingelements to output the gate control signal to the inverter 545.

The control device 100 generates a torque command value based on thesteering torque or the like, and controls the torque and the rotationspeed of the motor 543 by, for example, vector control. The controldevice 100 can perform not only the vector control but also otherclosed-loop control. The rotation speed is expressed by the number ofrevolutions (rpm) at which a rotor rotates per unit time (for example,one minute) or the number of revolutions (rps) at which the rotorrotates per unit time (for example, one second). The vector control is amethod in which current flowing through the motor is separated into acurrent component that contributes to generation of a torque and acurrent component that contributes to generation of a magnetic flux, andthe current components orthogonal to each other are independentlycontrolled.

The power supply circuit 111 is connected to an external power source(not illustrated) and generates DC voltage required for each block inthe circuit. The DC voltage to be generated is, for example, 3 V or 5 V.

The angle sensor 112 is, for example, a resolver or a Hall IC.Alternatively, the angle sensor 112 is also realized by a combination ofan MR sensor having a magnetoresistive (MR) element and a sensor magnet.The angle sensor 112 detects a rotation angle of the rotor to output therotation angle to the processor 200. The control device 100 may includea speed sensor and an acceleration sensor that detects the rotationspeed and acceleration of the motor instead of the angle sensor 112. Theprocessor 200 can calculate the angular velocity ω [rad/s] based on theelectrical angle θ_(m) of the motor.

The input circuit 113 receives a motor current value (hereinafter,referred to as an “actual current value”) detected by a current sensor(not illustrated), converts a level of the actual current value into aninput level for the processor 200 as needed, and outputs the actualcurrent value to the processor 200. A typical example of the inputcircuit 113 is an analog-digital conversion circuit.

The processor 200 is a semiconductor integrated circuit and is alsoreferred to as a central processing unit (CPU) or a microprocessor. Theprocessor 200 sequentially executes a computer program which is storedin the ROM 116 and describes a command set for controlling motordriving, and realizes desired processing. In addition to or instead ofthe processor 200, the control device 100 includes a field programmablegate array (FPGA), a graphics processing unit (GPU), an applicationspecific integrated circuit (ASIC), or an application specific standardproduct (ASSP) on which a CPU is mounted, or a combination of two ormore circuits selected from these circuits. The processor 200 sets acurrent command value according to the actual current value, therotation angle of the rotor, and the like, generates a pulse widthmodulation (PWM) signal, and outputs the PWM signal to the drivingcircuit 115.

The communication I/F 114 is an input/output interface configured totransmit and receive data in conformity with an in-vehicle control areanetwork (CAN), for example.

The driving circuit 115 is typically a gate driver (or a pre-driver).The driving circuit 115 generates a gate control signal in accordancewith the PWM signal and gives the gate control signal to gates of theplurality of switching elements included in the inverter 545. There is acase where a gate driver is not necessarily required when a drivingtarget is a motor that can be driven at a low voltage. In this case, theprocessor 200 may have the function of the gate driver.

The ROM 116 is electrically connected to the processor 200. The ROM 116is a writable memory (for example, a PROM), a rewritable memory (forexample, a flash memory or an EEPROM), or a read-only memory, forexample. The ROM 116 stores a control program including a command setfor causing the processor 200 to control motor driving. For example, thecontrol program is temporarily expanded in a RAM (not illustrated) atthe time of booting.

FIG. 3 illustrates functional blocks of the processor 200 forcontrolling the motor according to the example embodiment of the presentdisclosure. In the illustrated implementation example, the processor200, which is a computer, sequentially executes processing (or tasks)necessary for controlling the motor by using a torque controller, amodel following controller, a subtractor, and an adder.

Each functional block is implemented in the processor 200 as software(or firmware) and/or hardware. The processing of each functional blockis typically described in a computer program in units of softwaremodules and stored in the ROM 116. However, in a case where an FPGA orthe like is used, all or some of the functional blocks may beimplemented as hardware accelerators. The motor control method accordingto the example embodiment of the present disclosure is implemented in acomputer, and can be implemented by causing the computer to execute adesired operation.

The control device 100 includes a torque controller 210, a modelfollowing controller 230, a subtractor AD1, and an adder AD2. In otherwords, functions corresponding to the torque controller 210, the modelfollowing controller 230, the subtractor AD1, and the adder AD2 areimplemented in the processor 200.

The torque controller 210 operates based on a steering torque T_(h) andgives an input to a control target 220 that is a motor. For example, thesteering torque T_(h) detected by the steering torque sensor 541 isinput to the torque controller 210. The torque controller 210 generatesa target motor torque (or torque command value) T_(ref) by applyingphase compensation to the steering torque T_(h) when the steeringfrequency or the steering speed is within a predetermined range, andinputs the target motor torque T_(ref) to the control target 220.

The torque controller 210 illustrated in FIG. 3 includes a base assistcalculation unit 211 and a phase compensator 212.

The base assist calculation unit 211 acquires the steering torque T_(h)and the vehicle speed. The base assist calculation unit 211 generates abase assist torque based on the steering torque T_(h) and the vehiclespeed. For example, the base assist calculation unit 211 can include alook-up table (LUT) that defines a correspondence between the steeringtorque T_(h), the vehicle speed, and the base assist torque. The baseassist calculation unit 211 can determine the base assist torque havinga correspondence relationship based on the steering torque T_(h) and thevehicle speed with reference to the LUT. Furthermore, the base assistcalculation unit 211 can determine the base assist gain based on theslope defined by the ratio of the change amount of the base assisttorque to the variation amount of the steering torque T_(h).

The phase compensator 212 in the example embodiment of the presentdisclosure adjusts the assist gain within a range of the steeringfrequency when the driver operates the steering wheel, and compensatesfor the rigidity of the torsion bar. In the example embodiment of thepresent disclosure, an example of the predetermined range is 5 Hz orless. The phase compensator 212 may apply, for example, first-orderphase compensation to the steering torque (torsion torque) when thesteering frequency is 5 Hz or less. The first-order phase compensationis expressed by, for example, a transfer function of the mathematicalexpression of Math. 1.

$\begin{matrix}{{C(s)} = \frac{{\frac{1}{2\pi f_{1}}s} + 1}{{\frac{1}{2\pi f_{2}}s} + 1}} & \left\lbrack {{Math}.1} \right\rbrack\end{matrix}$

where s is a Laplace transformer, f₁ is a frequency (Hz) of the zeropoint of the transfer function, and f₂ is a frequency (Hz) of the poleof the transfer function. A graph in which the gain (or loop gain) isset as a vertical axis and the logarithm of the frequency is set as ahorizontal axis is referred to as a gain diagram. In the gain diagram,the zero point means the intersection of the gain curve and thehorizontal axis indicating 0 dB, and the pole means the maximum point ofthe gain curve. For example, by setting the pole frequency to be higherthan the zero point frequency, a phase lead compensation can be applied.The longer the distance between the frequencies is, the larger theamount of phase lead is.

The phase compensator 212 generates a target motor torque T_(ref) basedon the base assist torque and the base assist gain output from the baseassist calculation unit 211. For example, the phase compensator 212 maybe a stabilization compensator and apply stability phase compensation tothe base assist torque. The phase compensator 212 may have asecond-order or higher transfer function whose frequency characteristicis variable according to the base assist gain. The second-order orhigher transfer function is expressed using a responsiveness parameter ωand a damping parameter ζ. The second-order or higher transfer functioncan be expressed by, for example, the mathematical expression of Math.2. By setting the order number of the transfer function to two, dampingcan be given to the characteristic of the transfer function. A phasecharacteristic can be adjusted by changing the damping.

$\begin{matrix}{{C(s)} = {\frac{s^{2} + {2\zeta_{1}\omega_{1}s} + \omega_{1}^{2}}{s^{2} + {2\zeta_{2}\omega_{2}s} + \omega_{2}^{2}}\left( \frac{\omega_{2}^{2}}{\omega_{1}^{2}} \right)}} & \left\lbrack {{Math}.2} \right\rbrack\end{matrix}$

where s is a Laplace transformer, ω₁ is a zero point frequency, ω₂ is apole frequency, ζ₁ is zero point damping, and ζ₂ is pole damping. Thepole frequency ω₂ is lower than the zero point frequency ω₁.

The model following controller 230 is configured to estimate thedisturbance torque based on the angular velocity ω (MR angular velocity)of the motor, which is the output from the control target 220, calculatethe estimated disturbance torque, and feed back the estimateddisturbance torque to the input to the control target 220. The torquefed back from the model following controller 230 to the input to thecontrol target 220 corresponds to a “correction torque” for correctingthe input to the control target 220. The model following controller 230generates the correction torque based on the output of the controltarget 220. An example of the model following controller 230 is a modelfollowing controller configured to perform model following control. Aspecific configuration of the model following controller 230 will bedescribed in detail later.

The subtractor AD1 subtracts the estimated disturbance torque outputfrom the model following controller 230 from the target motor torqueT_(ref). The output from the subtractor AD1 is input to the adder AD2and the model following controller 230. The adder AD2 adds thedisturbance torque T_(d) to the output from the subtractor AD1 to outputthe result to the control target 220. Here, examples of the disturbancein the example embodiment of the present disclosure include frictioncaused by a mechanism such as a motor or a deceleration gear, a torqueripple or a rattling, a self-aligning torque, or a disturbance that mayoccur when the vehicle travels on an unpaved rattling road or gravelroad. Here, the self-aligning torque means a torque that acts in adirection in which the steering wheel returns by the elasticity of thetire that is twisted when the steering wheel is turned.

The model following controller has an inverse plant model, a high-passfilter and a low-pass filter (or Q filter). The model followingcontroller is configured so that the transfer function P(s) of thecontrol target is constrained to the nominal model P_(n)(s) in afrequency band in which a gain in a gain characteristic of Q(s)·HPF(s)is 1 where Q(s) is a transfer function of the low-pass filter and HPF(s)is a transfer function of the high-pass filter. Note that, in thepresent specification, “the transfer function of the control target isconstrained to the nominal model” means that, for example, the controltarget is controlled such that the transfer function of the controltarget appears to be a transfer function of the nominal model inappearance when the input/output relationship is viewed.

FIG. 4 illustrates a configuration example of a model followingcontroller 230A in the first implementation example. The model followingcontroller 230A includes a control target inverse model 231, a low-passfilter 232, a high-pass filter 233, and a subtractor SU1. The high-passfilter 233 has a first cutoff frequency, and the low-pass filter 232 hasa second cutoff frequency.

The angular velocity ω of the motor is input to the control targetinverse model 231. The subtractor SU1 subtracts the output of thesubtractor AD1 from the output of the control target inverse model 231to generate an estimated disturbance torque {circumflex over ( )}T_(d).The estimated disturbance torque {circumflex over ( )}T_(d) is subjectedto a filtering process by the low-pass filter 232 and the high-passfilter 233 coupled in series in this order, and is input to thesubtractor AD1. As described above, the model following controller 230Afeeds back the estimated disturbance torque {circumflex over ( )}T_(d)to the input to the control target 220. Note that “{circumflex over( )}T_(d)” means T_(d) with a hat illustrated in FIGS. 4 and 12 .

The model following controller 230A executes model following controlthat means a feedback loop using the angular velocity ω of the motor,which is the control target 220, for an outer loop of current control.In the first implementation example, the torque ripple depending on theangular velocity ω can be compensated by the feedback loop formed by themodel following controller 230A. The signal of the angular velocity ωused for the control can be corrected for each type of the motor, andthe accuracy of the signal of the angular velocity ω can be improved ascompared with the current signal and the like. As a result, torqueripple compensation with high accuracy can be applied to torque control.

The model following controller 230A is structurally similar to aconventional disturbance estimator (or disturbance observer), but hasdifferent actions and effects. The conventional disturbance estimatorestimates the disturbance torque by selecting the inverse plant model toa value close to the plant model, adjusts the disturbance torque inadvance, and reduces the influence of the disturbance. The frequencyband to be compensated is a low frequency of 4 Hz or less that which maybe generated by the behavior of the vehicle.

The model following control according to the example embodiments of thepresent disclosure uses the effect of the feedback loop constraining theplant to the nominal model defined in the inverse plant model. Afrequency band to be compensated is about 4 Hz to 150 Hz, which isdifferent from a frequency band of a conventional disturbance estimator.For example, when the inverse plant model is defined so that there is notorque ripple, the plant model is constrained to the characteristicwithout torque ripple by the model following control, and as a result,the torque ripple can be reduced by applying torque ripple compensation.In addition, by constructing an inertia or viscosity model andconstraining the plant model to the model, a reduction in inertia orviscosity of the plant model can be realized. By performing the modelfollowing control, for example, the lost torque compensation or themotor inertia compensation is performed in addition to the compensationof the torque ripple of the motor.

In the present specification, the control target 220, the nominal model(or a plant model) used to constrain the control target 220, the controltarget inverse model 231 defined by an inverse plant model of the plantmodel, the transfer function of the low-pass filter 232, and thetransfer function of the high-pass filter 233 are described as P(s),P_(n)(s)_(r) P_(n) ⁻¹(s), Q(s), and HPF(s), respectively.

The plant model (nominal model) is expressed by the mathematicalexpression of Math. 3, and the inverse plant model is expressed by themathematical expression of Math. 4. By appropriately setting J_(mn) andB_(mn), a desired frequency characteristic can be given to P(s) of thecontrol target 220. In the present example embodiment, the plant model(nominal model) is a model of a one-inertia system.

$\begin{matrix}\frac{1}{{J_{m_{n}}s} + B_{m_{n}}} & \left\lbrack {{Math}.3} \right\rbrack\end{matrix}$ $\begin{matrix}{{J_{m_{n}}s} + B_{m_{n}}} & \left\lbrack {{Math}.4} \right\rbrack\end{matrix}$

A complementary sensitivity function of the inner loop configured by themodel following controller is defined as T(s), and a modeling error ofthe plant model is defined as Δ(s). T(s) is expressed by Q(s)·HPF(s),and the relationship shown in Math. 5 is established with respect toΔ(s). The robust stability of the model following controller is securedwhen the small gain theorem expressed by the mathematical expression ofMath. 6 holds between T(s) and Δ(s). In order to suppress disturbance,it is sufficient when T(s)=1, but in consideration of robust stability,it is necessary to satisfy the mathematical expression of Math. 6. Asunderstood from this, disturbance suppression and robust stability arenot compatible.

$\begin{matrix}{{P(s)} = {\frac{1}{{J_{m_{n}}s} + B_{m_{n}}}\left( {1 + {\Delta(s)}} \right)}} & \left\lbrack {{Math}.5} \right\rbrack\end{matrix}$ $\begin{matrix}{{{❘{T\left( {j\omega} \right)}❘} < {\frac{1}{❘{\Delta\left( {j\omega} \right)}❘}{or}{❘{{T\left( {j\omega} \right)}{\Delta\left( {j\omega} \right)}}❘}} < 1},{{\forall s} = {j\omega}}} & \left\lbrack {{Math}.6} \right\rbrack\end{matrix}$

FIG. 5 illustrates a gain diagram of a transfer function of the entiresteering system. In the gain diagram, the horizontal axis represents thefrequency [Hz] and the vertical axis represents the gain [dB]. In thefirst implementation example, in order to realize the disturbancesuppression by the frequency band, the frequency band is divided into aregion I in which the disturbance suppression is necessary and T(s)=1,and a region II in which T(s) is lowered to ensure the robust stability.In the region II, 1/Δ(s)>T(s) holds.

The gain characteristic of the transfer function of the entire steeringsystem has peaks around 20 Hz and around 50 Hz, for example, and themodeling error appears at a peak around 50 Hz of the two peaks. That is,Δ(s) has a peak around 50 Hz, and 1/Δ(s) shown in FIG. 5 has a bottomaround 50 Hz. As a gain characteristic adjustment method, there areadjustment of 1/Δ(s) and adjustment of a break point of T(s). Theadjustment of 1/Δ(s) is performed by adjusting J_(mn) and B_(mn) of theplant model, and the adjustment of the break point of T(s) is performedby adjusting the second cutoff frequency of the low-pass filter 232.Furthermore, the sensitivity to disturbance can be adjusted by thesteering assist amount, the steering speed, or the vehicle speed. In acase where the frequency of the bottom of the modeling error is close tothe frequency of the boundary between the region I and the region II, asa countermeasure, a method of raising the order of the low-pass filter232 to sharply lower T(s) in the region I where disturbance suppressionis necessary is often used.

The control device 100 performs torque control on a low-frequency torquesignal and performs control such that the angular velocity ω≈0 on a highfrequency disturbance, thereby realizing stabilization of steering sothat the uncontrollable steering wheel is generated. In order to achievethis object, the control device 100 decreases the high frequency gain ofthe torque control using the torque controller 210, and constrains thecontrol target P(s) to the characteristic in which the high frequencygain decreases using the model following controller 230A. The reason forperforming the latter process is to prevent the control target 220 fromreacting to a disturbance such as T_(d) illustrated in FIG. 4 when thedisturbance is input to the control target 220.

FIG. 6 illustrates a gain diagram of the transfer function C(s) of thephase compensator 212 in the torque controller 210. FIG. 7 illustrates again diagram of the transfer function HPF(s) of the high-pass filter233. FIG. 8 illustrates a gain diagram of the nominal model P_(n)(s). Inthe gain diagram, the horizontal axis represents the frequency [Hz] andthe vertical axis represents the gain [dB]. For example, when the phasecompensator 212 having the gain characteristic of the transfer functionC(s) illustrated in FIG. 6 is applied, the high frequency gain can bereduced in the gain characteristic of the nominal model P_(n)(s) asillustrated in FIG. 8 . The cutoff frequency fc in the gain diagram ofthe transfer function C(s) is, for example, 2 Hz or more and 10 Hz orless, and the cutoff frequency fc in the gain diagram of P_(n)(s) is,for example, 2 Hz or more and 20 Hz or less.

The model following controller 230A is configured so that the transferfunction P(s) of the control target 220 is constrained to the nominalmodel P_(n)(s) in the frequency band in which the gain in the gaincharacteristic of Q(s)·HPF(s) is 1. The inverse plant model P_(n) ⁻¹(s)is designed to give an inverse characteristic for which constrain isdesired and to take advantage of the gain characteristics ofQ(s)·HPF(s). By appropriately designing J_(mn) and B_(mn) of the plantmodel, as illustrated in FIG. 8 , gain characteristics of the nominalmodel P_(n)(s) whose gain decreases in a high frequency region can beobtained. The frequency of the boundary between the region I and theregion II (the lower limit value of the frequency range defining theregion I) is the maximum frequency that can be input by the driver, andis generally about 2 Hz to 10 Hz. This frequency depends on the firstcutoff frequency of the high-pass filter 233. Therefore, the lower limitfrequency of the effective range of the model following control isdetermined by adjusting the first cutoff frequency of the high-passfilter 233 so as not to disturb the torque control.

The low-pass filter 232 and the high-pass filter 233 are coupled inseries. The low-pass filter 232 may include a multistage LPF. That is,Q(s) can be expressed as a transfer function of the n-stage LPF (n is 1or more). The second cutoff frequency is larger than the first cutofffrequency. The first cutoff frequency is, for example, 2 Hz or more and10 Hz or less, and is preferably, for example, 5 Hz or more and 7 Hz orless. The second cutoff frequency is, for example, 3 Hz or more andpreferably 50 Hz or less. However, the upper limit of the second cutofffrequency can be set to about 140 Hz to 200 Hz. The cutoff frequency fcof the gain characteristic of the nominal model P_(n)(s) illustrated inFIG. 8 depends on the first cutoff frequency and the second cutofffrequency, and is, for example, 2 Hz or more and 20 Hz or less.

The present inventors confirmed the effect obtained by applying themodel following control according to the example embodiment of thepresent disclosure by performing actual vehicle measurement. In theactual vehicle measurement, the effect of reducing the torque ripple andgeneration of the uncontrollable steering wheel by applying the modelfollowing control to the torque control was measured. Here, generationof the uncontrollable steering wheel means that the steering wheelswings left and right when the vehicle passes over a step in a statewhere the hands does not grip the steering wheel.

FIG. 9 illustrates measurement results of the steering angle and thetorsion torque in a case where the model following control is notapplied. FIG. 10 illustrates measurement results of the steering angleand the torsion torque in a case where the model following control isapplied. In the graph, the horizontal axis represents the steering angle[deg] and the vertical axis represents the torsion torque [Nm]. Thegraph shows waveforms measured when steering is performed at an angularvelocity of 180 [deg/s] from end to end (from a state where the steeringwheel is fully turned to the left to a state where the steering wheel isfully turned to the right, or vice versa).

When the portion surrounded by the alternate long and short dash line ofthe graph is enlarged, it has been found that the torque ripple in thecase where the model following control is applied can be suppressed, ascompared with the case where the model following control is not applied.Specifically, it has been found that the variation amount of the torsiontorque decreases by about 0.1 [Nm].

FIG. 11 illustrates measurement results of the temporal change in thesteering angle in each of a case where the model following control isnot applied and a case where the model following control is applied. Inthe graph, the horizontal axis represents time [sec], and the verticalaxis represents a steering angle [deg]. The region of the time when thevehicle has passed over the step is indicated by a dashed rectangle. Ithas been found that, by applying the model following control to thetorque control, the change in the steering angle when the vehicle passesover the step is suppressed, and generation of the uncontrollablesteering wheel can be appropriately reduced.

According to the first implementation example, the high frequencycomponent of the disturbance can be reduced by applying the modelfollowing control to the torque control. As a result, it is possible toappropriately reduce the torque ripple that may occur when the vehicleis steered and generation of the uncontrollable steering wheel that mayoccur when the vehicle passes over the step.

Next, the model following controller according to the secondimplementation example will be described with reference to FIGS. 12 to14 . The model following controller according to the secondimplementation example is different from the model following controlleraccording to the first implementation example in that it has a frictioncompensation calculator. Differences from the model following controlleraccording to the first implementation example will be mainly describedbelow.

Since the disturbance estimated by the model following controllerincludes friction of a mechanism such as a motor and a decelerationgear, the model following controller according to the secondimplementation example is configured to extract a friction componentfrom the estimated disturbance torque and apply friction compensation tothe estimated disturbance torque. Friction compensation is, for example,for friction of the motor, friction of the deceleration gear, or aright/left difference in friction of the deceleration gear.

When conventional friction compensation control is to be applied, whenthe angular velocity ω of the motor is near zero, a change in thefriction compensation torque (Nm) with respect to the angular velocity ωof the motor has to be made gentle in order to prevent chattering, andas a result, highly accurate friction compensation control cannot beperformed in some cases. According to the study of the inventor, inorder to solve this problem, it is desirable to sequentially estimateand compensate for friction.

The model following controller according to the second implementationexample is configured to feed back the disturbance compensation torqueto the input to the control target. Specifically, the model followingcontroller includes a high-pass filter that removes a low frequencycomponent from the estimated disturbance torque, a friction compensationcalculator that is coupled in parallel to the high-pass filter to applyfriction compensation to the estimated disturbance torque to calculatean estimated value of the mechanical friction torque, and an adder thatadds the estimated value of the friction torque to the estimateddisturbance torque from which the low frequency component was removed bythe high-pass filter to generate a disturbance compensation torque. Inthe second implementation example, the estimated disturbance torquecorresponds to “first correction torque”, and the disturbancecompensation torque corresponds to “second correction torque”.

FIG. 12 illustrates a configuration example of a model followingcontroller 230B in the second implementation example. The modelfollowing controller 230B is configured to perform the model followingcontrol as in the model following controller 230A according to the firstimplementation example. However, the function of the model followingcontrol is not essential.

The model following controller 230B includes a friction compensationcalculator 250. The friction compensation calculator 250 is coupled inparallel to the high-pass filter 233, and calculates an estimated valueof the mechanical friction torque by applying friction compensation tothe estimated disturbance torque {circumflex over ( )}T_(d). Thefriction compensation calculator 250 includes a subtractor 251, alimiter 252, and a gain adjuster 253. The subtractor 251 subtracts theoutput value from the high-pass filter 233 from the output value fromthe low-pass filter 232. The limiter 252 limits the output value fromthe subtractor 251. When the input value exceeds the upper limit orlower limit threshold value, the limiter 252 clips the input value tothe upper limit or lower limit threshold value.

The gain adjuster 253 multiplies the output value from the limiter 252by the gain K. The maximum value of the gain K of the gain adjuster 253is determined under the condition that the transfer function of thecontrol target 220 is constrained to the nominal model. The maximumvalue of the gain K is set to, for example, about 1 to 1.2.

The estimated disturbance torque {circumflex over ( )}T_(d) includesmechanical friction. In the estimation of the disturbance, the frictionis first estimated from the transmission path of the output torque ofthe motor, and then the torque acting on the motor such as theself-aligning torque is estimated. Therefore, the friction compensationcalculator 250 calculates a value corresponding to the friction torquein the disturbance estimated first as an estimated value of the frictiontorque. In general, since appropriate friction is required for the EPS,it is possible to realize highly accurate friction compensation whilemaintaining appropriate frictional force by setting a value smaller thanthe frictional force actually acting to an estimated value of thefriction torque.

In order to apply friction compensation to the estimated disturbancetorque used for the model following control, it is necessary to payattention to the stability condition of the model following control.This condition is that the gain in the gain characteristic of thetransfer function of the friction compensation calculator 250constrained to the characteristic in which the stability is considereddoes not exceed 1 based on the above-described small gain theorem. Thisis derived from the design condition of the low-pass filter 232. In thesecond implementation example, the subtractor 251 is provided in a stagebefore the limiter 252 so that the value of the friction compensationgain, that is, the gain K, is set to 1 at maximum so as to constantlysatisfy this condition, and the gain in the gain characteristic is setto 1 under this condition, and the subtraction processing is applied. Inother words, the friction compensation calculator 250 behaves as alow-pass filter having a transfer function of 1-HPF(s).

The estimated disturbance torque {circumflex over ( )}T_(d) includes alow frequency component {circumflex over ( )}T_(d1), a medium frequencycomponent {circumflex over ( )}T_(d2), and a high frequency component{circumflex over ( )}T_(d3). The low-pass filter 232 removes the highfrequency component {circumflex over ( )}T_(d3) from the estimateddisturbance torque {circumflex over ( )}T_(d), and the high-pass filter233 further removes the low frequency component {circumflex over( )}T_(d1) from the estimated disturbance torque {circumflex over( )}T_(d). As described above, friction compensation is only for themedium frequency component {circumflex over ( )}T_(d2) of the estimateddisturbance torque in the range from the first cutoff frequency of thehigh-pass filter 233 to the second cutoff frequency of the low-passfilter 232. However, since the assumed friction included in thedisturbance is a low frequency component of the disturbance, the lowfrequency component {circumflex over ( )}T_(d1) is not subject tofriction compensation according to the filtering process describedabove. Therefore, by coupling the friction compensation calculator 250in parallel to the high-pass filter 233, the low frequency component{circumflex over ( )}T_(d1) of the disturbance that has been subjectedto the filtering process by the high-pass filter 233 and is no longercompensated is added again to the estimated disturbance torque{circumflex over ( )}T_(d), thereby realizing friction compensation.More specifically, the friction compensation calculator 250 adds a valueobtained by multiplying the low frequency component {circumflex over( )}T_(d1) by the gain K to the medium frequency component {circumflexover ( )}T_(d2) to generate the disturbance compensation torque. Notethat “{circumflex over ( )}T_(d1)” means T_(d1) with the hat illustratedin FIG. 12 , “{circumflex over ( )}T_(d2)” means T_(d2) with the hatillustrated in FIG. 12 , and “{circumflex over ( )}T_(d3)” means T_(d3)with the hat illustrated in FIG. 12 .

A vehicle equipped with the EPS is capable of traveling according to atravel mode having an automatic driving mode and a manual driving mode.In this case, the gain K of the gain adjuster 253 may be switchedaccording to the travel mode. The greater the gain K, the greater thedegree of friction reduction. The gain K set in the automatic drivingmode is preferably larger than the gain K set in the manual drivingmode. As a result, it is possible to apply optimum friction compensationto an automatic driving mode in which a reduction in friction is morerequired.

The model following controller 230B further includes an adder AD3. Theadder AD3 adds the output value from the gain adjuster to the outputvalue from the high-pass filter 233. The output from the adder AD3 isfed back to the input to the control target 220 as a disturbancecompensation torque.

An auxiliary device that recognizes a lane such as a white line or ayellow line when traveling on an expressway and assists automatictraveling of a vehicle following the lane has been developed. It isknown that, in a vehicle equipped with an EPS and an auxiliary device,when there is a right/left difference in friction of a decelerationgear, the control of the auxiliary device that causes the vehicle totravel straight along the center of a lane can be affected. According tothe friction compensation control according to the example embodiment ofthe present disclosure, even in a case where there is a right/leftdifference in friction of the deceleration gear, it is possible tosequentially calculate an estimated value of the friction torque, andthus, it is possible to solve the above problem. Note that the angularvelocity ω of the motor, which is the output of the plant model,includes information on a right/left difference in friction of thedeceleration gear.

The present inventors confirmed the effect obtained by applying thefriction compensation control by the gain adjustment through simulation.The effect of reducing friction by friction compensation control wasmeasured by simulation.

FIG. 13 illustrates the simulation result of the steering angle and thesteering torque in each of a case where the friction compensationcontrol by gain adjustment is not applied and a case where the frictioncompensation control by gain adjustment is applied. In the graph, thehorizontal axis represents the steering angle [deg], and the verticalaxis represents the steering torque [Nm]. A graph indicated by a brokenline indicates a waveform when the friction compensation control is notapplied, and a graph indicated by a solid line indicates a waveform whenthe friction compensation control is applied. An arrow in the drawingindicates the width of the steering torque, and the width corresponds tothe magnitude of friction. It has been found that friction can beappropriately reduced by applying friction compensation control.

FIG. 14 illustrates the simulation result of the steering angle and thesteering torque in each of a case where the conventional frictioncompensation control is applied and a case where the frictioncompensation control by gain adjustment is applied. In the graph, thehorizontal axis represents the steering angle [deg], and the verticalaxis represents the steering torque [Nm]. A graph indicated by a brokenline indicates a waveform when the conventional friction compensationcontrol is applied, and a graph indicated by a solid line indicates awaveform when the friction compensation control by gain adjustment isapplied. According to the conventional friction compensation control, asdescribed above, when the angular velocity ω of the motor is near zero,the change in the friction compensation torque (Nm) with respect to theangular velocity ω of the motor has to be made gentle in order toprevent chattering. Due to this, a spike was observed in the steeringtorque when turning the steering wheel over (see the portion surroundedby the dashed circle in the figure). On the other hand, when thefriction compensation control by gain adjustment was applied, no spikewas confirmed, and it was found that the friction was appropriatelyreduced.

According to the second implementation example, by further applyingfriction compensation control by gain adjustment to torque control, itis possible to appropriately reduce friction while reducing a highfrequency component of disturbance.

In the third implementation example, the control target includes asteering wheel 521, universal joints 523A and 523B, a rotation shaft524, a torsion bar 546, a motor 543, and a deceleration gear 544. Sincethe control target in the third implementation example includes portionsthat can rotate relative to each other via the torsion bar 546, themotion of the control target cannot be described only by a simpleequation of motion of the one-inertia system. The control target in thethird implementation example changes between the one-inertia system andthe two-inertia system depending on the strength with which the driverof the vehicle grips the steering wheel 521. The stronger the drivergrips the steering wheel 521, the closer the control target is to the1-inertia system. The weaker the driver grips the steering wheel, thecloser the control target is to the two-inertia system. In the thirdimplementation example, an angular velocity corresponding to the angularvelocity of the deceleration gear 544 is input to the model followingcontroller as an output of the control target.

In the third implementation example, the plant model (nominal model) isa model having frequency characteristics between the one-inertia systemand the two-inertia system. The transfer function P_(n)(s) of the plantmodel (nominal model) in the third implementation example is expressedby the mathematical expression of Math. 7, and the transfer functionP_(n) ⁻¹(s) of the inverse plant model is expressed by the mathematicalexpression of Math. 8.

$\begin{matrix}{\frac{1}{{J_{{STG}_{n}}s} + B_{{STG}_{n}}}\frac{s^{2} + {2\zeta_{1n}\omega_{1n}s} + \omega_{1n}^{2}}{s^{2} + {2\zeta_{2n}\omega_{2n}s} + \omega_{2n}^{2}}} & \left\lbrack {{Math}.7} \right\rbrack\end{matrix}$ $\begin{matrix}{\left( {{J_{{STG}_{n}}s} + B_{{STG}_{n}}} \right)\left( \frac{s^{2} + {2\zeta_{2n}\omega_{2n}s} + \omega_{2n}^{2}}{s^{2} + {2\zeta_{1n}\omega_{1n}s} + \omega_{1n}^{2}} \right.} & \left\lbrack {{Math}.8} \right\rbrack\end{matrix}$

In the mathematical expression of Math. 7 and the mathematicalexpression of Math. 8, s is a Laplace transformer, J_(STGn) is aparameter representing the inertia moment of the nominal model, B_(STGn)is a parameter representing the viscous friction coefficient of thenominal model, ω_(1n) is the frequency of the zero point of the transferfunction P_(n)(s), ω_(2n) is the frequency of the pole of the transferfunction P_(n)(s), ζ_(1n) is the damping ratio at the zero point of thetransfer function P_(n)(s), and ζ_(2n) is the damping ratio at the poleof the transfer function P_(n)(s).

In the third implementation example, the nominal model is a model havingfrequency characteristics between the one-inertia system and thetwo-inertia system. The mathematical expression of Math. 7 expressingthe transfer function P_(n)(s) of the nominal model is an expressionobtained by adding an attenuation term to an expression representing thetwo-inertia system. In the mathematical expression of Math. 7, theattenuation terms are 2ζ_(1n)ω_(1n)s and 2ζ_(2n)ω_(2n)s. The expressionobtained by removing these attenuation terms from the mathematicalexpression of Math. 7 is an expression representing the two-inertiasystem. In the third implementation example, the degree of the transferfunction P_(n)(s) of the nominal model is 3.

In the third implementation example, the nominal model is a model inwhich mechanical characteristics when a driver (steering person) steersthe steering wheel 521 are considered. The control target approaches theone-inertia system as the driver strongly grips the steering wheel 521,and approaches the two-inertia system as the driver weakly grips thesteering wheel 521. Therefore, the transfer function P(s) of the controltarget in the third implementation example changes between theone-inertia system and the two-inertia system depending on how a forceis applied from the driver's arm to the steering wheel 521. In the thirdimplementation example, by setting the nominal model as a model havingfrequency characteristics between the one-inertia system and thetwo-inertia system, it is possible to prevent the modeling error Δ(s)between the transfer function P_(n)(s) of the nominal model and thetransfer function P(s) of the control target from becoming too largeregardless of the state of the control target between the one-inertiasystem and the two-inertia system. Therefore, the control target can besuitably controlled using the nominal model regardless of how the driversteers the steering wheel 521. As described above, in the thirdimplementation example, the nominal model is a model in consideration ofmechanical characteristics given to the control target by the way thedriver grips the steering wheel 521. The control device 100 in the thirdimplementation example can suitably control the control target by havingsuch a nominal model as an internal model. Other configurations in thethird implementation example can be similar to those in the otherimplementation examples described above.

The example embodiments of the present disclosure can be used for amotor control device for controlling an EPS mounted on a vehicle.

Features of the above-described example embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While example embodiments of the present disclosure have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present disclosure. The scope of the presentdisclosure, therefore, is to be determined solely by the followingclaims.

What is claimed is:
 1. A control device usable in an electric powersteering device including a motor to control the motor, the controldevice comprising: a torque controller to operate based on steeringtorque and to provide an input to a control target that is the motor;and a model following controller to generate a first correction torquebased on an output from the control target; wherein the model followingcontroller includes: a high-pass filter to remove a low frequencycomponent from the first correction torque; a friction compensationcalculator coupled in parallel to the high-pass filter to apply frictioncompensation to the first correction torque to calculate an estimatedvalue of a mechanical friction torque; and an adder to add the estimatedvalue of the friction torque to the first correction torque from whichthe low frequency component is removed by the high-pass filter togenerate a second correction torque, and to feed back the secondcorrection torque to an input to the control target.
 2. The controldevice according to claim 1, wherein the model following controllerincludes a low-pass filter that is coupled in series to the high-passfilter to remove a high frequency component from the first correctiontorque; and the high-pass filter has a first cutoff frequency and thelow-pass filter has a second cutoff frequency larger than the firstcutoff frequency.
 3. The control device according to claim 2, whereinthe model following controller is configured or programmed so that atransfer function of the control target is constrained to a nominalmodel in a frequency band in which a gain in a gain characteristic ofQ(s)·HPF(s) is 1 where Q(s) is a transfer function of the low-passfilter and HPF(s) is a transfer function of the high-pass filter.
 4. Thecontrol device according to claim 3, wherein the friction compensationcalculator includes: a subtractor to subtract an output value from thehigh-pass filter from an output value from the low-pass filter; alimiter to limit an output value from the subtractor; and a gainadjuster to multiply an output value from the limiter by a gain; and theadder to add an output value from the gain adjuster to the output valuefrom the high-pass filter.
 5. The control device according to claim 4,wherein a maximum value of a gain of the gain adjuster is determinedunder a condition that the transfer function of the control target isconstrained to the nominal model.
 6. The control device according toclaim 3, wherein the first cutoff frequency is about 2 Hz or more andabout 10 Hz or less.
 7. The control device according to claim 6, whereinthe second cutoff frequency is about 3 Hz or more.
 8. The control deviceaccording to claim 1, wherein the torque controller is configured orprogrammed to generate a target motor torque by applying phasecompensation to the steering torque when a steering frequency is withina predetermined range, and to input the target motor torque to thecontrol target.
 9. The control device according to claim 4, wherein avehicle equipped with the electric power steering device is capable oftraveling according to a travel mode including an automatic driving modeand a manual driving mode, and a gain of the gain adjuster is switchedaccording to the travel mode.
 10. A motor module comprising: a motor;and the control device according to claim
 1. 11. An electric powersteering device comprising the motor module according to claim
 10. 12. Acomputer-implemented method for controlling a motor of an electric powersteering device including the motor, the method comprising: acquiring asteering torque; determining an operation amount based on the steeringtorque and inputting the operation amount to a control target that isthe motor; generating a first correction torque based on an output fromthe control target; removing a low frequency component from the firstcorrection torque; applying friction compensation to the firstcorrection torque to calculate an estimated value of a mechanicalfriction torque; adding the estimated value of the friction torque tothe first correction torque from which the low frequency component isremoved to generate a second correction torque; and feeding back thesecond correction torque to an input to the control target.